Hydraulic cylinder

ABSTRACT

A single-acting type hydraulic cylinder which is operated to be expanded and contracted by supply and discharge of liquid pressure from a so-called bottom side, in which the desired operation is permanently secured without bringing forth abrasion of a bearing or damage of a dust seal caused by rust or scratch in the outer circumference of a rod body.  
     A hydraulic cylinder which is operated to be expanded and contracted by supply and discharge of liquid pressure P to a liquid chamber R partitioned on the bottom side within a cylinder body  1 , characterized in that a head member  4  forming an open end of the cylinder body  1  is provided with a lubrication means  7  in sliding contact with the outer circumference of a rod body  3  and an oil seal  8  in series between a bearing  5  and a dust seal  6.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a hydraulic cylinder, andparticularly to an improvement in a single-acting type hydrauliccylinder suitable for use with a forklift.

[0002] In the past, a single acting type hydraulic cylinder for aforklift is operated to be extended, for example, as shown in FIG. 2,when liquid pressure P is supplied from the outside to a liquid chamberR which is a chamber on the counter rod side partitioned by a piston 2slidably inserted into a cylinder body 1.

[0003] Further, the hydraulic cylinder is operated to be contracted whena supply of liquid pressure P to the liquid chamber R is releasedwhereas a rod body 3 having a proximal end connected to the piston 2gets into the cylinder body 1 due to own weight or load exerting on theextreme end to contract the liquid chamber R through the piston 2.

[0004] At this time, the rod side chamber partitioned by the piston 2within the cylinder body 1 which is an air chamber A is in many casescommunicated with the atmosphere outside the cylinder body 1 through acommunication hole 1 a bored in the cylinder body 1.

[0005] On the other hand, the rod body 3 which moves in and out of thecylinder body 1 extends through an axial part of a head member 4 formingan open end of the cylinder body 1. At this time, a bearing 5 forcausing the outer circumference of the rod body 3 to sliding contacttherewith is disposed in the inner circumference internally of thecylinder body 1 in the head member 4, and a dust seal 6 for causing theouter circumference of the rod body 3 to sliding contact therewith isdisposed in the inner circumference of an open end in the head member 4.

[0006] Therefore, in the hydraulic cylinder, for example, when it isused for a forklift, a fork loaded with baggage can be moved up by theextension action thereof, and the fork loaded with baggage can be moveddown by the contraction action thereof. At this time, when the rod body3 is moved in and out of the cylinder body 1, the bearing 5 compensatesfor slidability of the rod body 3 with respect to the head member 4whereas the dust seal 6 wipes out so-called dust adhered to the outercircumference of the rod body 3 so that dust is not drawn into thecylinder body 1.

[0007] However, the conventional hydraulic cylinder shown in FIG. 2involves a fear that when the rod body 3 is moved in and out of thecylinder body 1, so-called heat generation occurs, and rust,discoloration and scratch due to the heat generation appear on the outercircumference of the rod body 3.

[0008] That is, in the above-described hydraulic cylinder, since the rodside chamber partitioned by the piston 3 within the cylinder body 1comprises the air chamber A, so-called dry is formed between the innercircumference of the bearing 5 and the outer circumference of the rodbody 3, tending to poor lubrication as compared with the case ofso-called wet where an oily sliding coating is formed.

[0009] Therefore, when sliding movement is frequently repeated betweenthe rod body 3 and the bearing 5, particularly when sliding movementsuch that the rod body 3 is pressed against the bearing 5 is repeated, aheat generation phenomenon tends to appear between the innercircumference of the bearing 5 and the outer circumference of the rodbody 3.

[0010] Then, when the heat generation phenomenon appears, a degenerationis brought forth in the outer circumference of the rod body 3 due to theheat generation, and rust or discoloration appears on the outercircumference of the rod body 3 due to the degeneration.

[0011] At this time, also in the bearing 5, abrasion is accelerated todeteriorate a function of bearing, and scratched phenomenon appears onthe outer circumference of the rod body 3, resulting in damage of eventhe dust seal 6.

[0012] As a consequence, occurrence of rust or formation of scratches inthe outer circumference of the rod body 3 further lowers so-calledslidability of the rod body 3 with respect to the cylinder body 1,posing an inconvenience being impossible to expect the desired permanentoperation of the hydraulic cylinder.

SUMMARY OF THE INVENTION

[0013] The present invention has been created in view of theabovedescribed circumstances, and has its object to provide asingle-acting type hydraulic cylinder which is operated to be expandedand contracted by supply and discharge of liquid pressure from so-calledbottom side, the hydraulic cylinder being optimum for permanentlysecuring the desired operation without bringing forth abrasion of abearing and damage of a dust seal caused by rust or scratch in the outercircumference of a rod body.

[0014] For achieving the aforementioned object, the present inventionprovides a hydraulic cylinder fundamentally constituted such that thecylinder is operated to be extended when liquid pressure from outside issupplied to a liquid chamber which is a counter rod side chamberpartitioned by a piston slidably inserted into a cylinder body, thecylinder is operated to be contracted when a supply of liquid pressureto the liquid chamber is released whereas a rod body having a proximalend connected to a piston is moved into the cylinder body due to ownweight or load exerting on the extreme end, and a head member forming anopen end of a cylinder body for moving in and out of the rod body has abearing for causing the outer circumference of the rod body to slidingcontact therewith and a dust seal, the hydraulic cylinder, in the headmember, comprising in series, a lubrication means in sliding contactwith the outer circumference of the rod body on the bearing side betweenthe bearing and the dust seal, and an oil seal in sliding contact withthe outer circumference of the rod body on the dust seal side.

[0015] In the above-described constitution, more concretely, thelubrication means is that for example, a lubricating material such asgrease is stored in an inner circumferential groove at a predeterminedposition formed in the inner circumference of the head member, or asuitable impregnate material is received in the inner circumferentialgroove, the impregnate material being impregnated with a suitablelubricating material.

[0016] Further, the rod side chamber partitioned by a piston within thecylinder body comprising an air chamber is communicated with theatmosphere outside the cylinder body through a communication hole boredin the cylinder body, or is set to an air spring chamber having a sealconstruction not in communication with the atmosphere outside thecylinder body while being an air chamber.

DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a partly cutaway cross sectional view of a hydrauliccylinder according to one embodiment of the present invention.

[0018]FIG. 2 is a partly cutaway cross sectional view of a conventionalhydraulic cylinder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0019] In the following, the present invention will be described on thebasis of an embodiment shown in the figure. As shown in FIG. 1, thehydraulic cylinder according to the present invention is alsoconstituted fundamentally similar to the aforementioned conventionalhydraulic cylinder, which is set to a single-acting hydraulic cylinderoperated to be expanded and contracted by a supply and discharge ofliquid pressure P from so-called bottom side.

[0020] Therefore, in the following description, with respect to theconstitution similar to that of the prior art shown in FIG. 2, partsthereof are designated by the same reference numerals in the figureexcept those as necessary, details of which are omitted.

[0021] That is, in the hydraulic cylinder according to the presentinvention, a bearing 5 is provided in the inner circumference inside acylinder body 1 in a head member 4, and a dust seal 6 is provided in theinner circumference of an open end in the head member 4. A lubricationmeans 7 and an oil seal 8 are provided in series between the bearing 5and the dust seal 6, that is, in series in an axial direction of a rodbody 3.

[0022] At this time, in the inner circumference of the head member 4,the lubrication means 7 is located on the bearing 5 side, that is, onthe air chamber A side within the cylinder body 1 whereas the oil seal 8is located on the dust seal 6 side, that is, on the external side of thecylinder body 1 to prevent the lubrication effect of the lubricationmeans from so-called escaping outside the cylinder body 1 by the oilseal 8.

[0023] Incidentally, in the illustration, the lubrication means 7stores, for example, a lubricating material 7 a such as grease within aninner circumferential groove 4 a at a predetermined position formed inthe inner circumference of the head member 4.

[0024] Incidentally, the lubrication means 7 will suffice, as a result,to form a lubricating coating (not shown and not designated by symbol)between the inner circumference of the bearing 5 and the outercircumference of the rod body 3. Therefore, in place of theabove-described constitution, a suitable impregnate material may bereceived in the inner circumferential groove 4 a, and a suitablelubricating material, that is, the lubricating material 7 a such asgrease described above may be impregnated in the impregnate material.

[0025] On the other hand, since the oil seal 8 comprises a so-called Upacking received in an inner circumferential groove 4 b at apredetermined position formed in the inner circumference of the headmember 4 similar to the above-described inner circumferential groove 4a, the inner circumference of which comes in sliding contact with theouter circumference of the rod body 3.

[0026] At this time, the oil seal 8 has a function such that alubrication coating from the internal side of the cylinder body 1adhered to the outer circumference of the rod body 3, that is, from thelubrication means 7 side is remained on the lubrication means 7 side soas to prevent the coating from flowing out to the external side of thecylinder body 1, that is, to the dust seal 6 side.

[0027] Therefore, the hydraulic cylinder according to the presentinvention is operated to be extended, for example, when it is used for aforklift, when liquid pressure P from the outside is supplied to aliquid chamber R partitioned by a piston 2 within the cylinder body 1,at which time a fork loaded with baggage is to be moved up.

[0028] Further, when likewise it is used for a forklift, a supply ofliquid pressure P to the liquid chamber R is released, whereas thehydraulic cylinder is operated to be contracted when the rod body 3 ismoved into the cylinder body 1 due to a load such as own weight, atwhich time a fork loaded with baggage is to be moved down.

[0029] In the foregoing, the air chamber A which is a rod side chamberpartitioned within the cylinder body 1 is communicated with theatmosphere outside the cylinder body 1 through a communication hole 1 abored in the cylinder body 1, and therefore, the above-describedexpansion and contraction operation is realized without so-calledresistance.

[0030] Further, at the time of the above-described expansion andcontraction, that is, at the time when the rod body 3 is moved in andout of the cylinder body 1, the outer circumference of the rod body 3comes in sliding contact with not only the bearing 5 and the dust seal 6disposed in the inner circumference of the head member 4 forming an openend of the cylinder body 1 but also the lubrication means 7 and the oilseal 8.

[0031] At this time, the bearing 5 secures slidability of the rod body 3with respect to the cylinder body 1 whereas the dust seal 6 preventsentry of dust adhered to the outer circumference of the rod body 3 intothe cylinder body 1.

[0032] At the same time, the lubrication means 7 forms a lubricationcoating between the inner circumference of the bearing 5 and the outercircumference of the rod body 3 to lower sliding friction therebetween,and the oil seal 8 is able to prevent the lubricating material 7 aforming a lubrication coating from escaping to the external side of thecylinder body 1, thus permanently securing lubrication between thebearing 5 and the rod body 3.

[0033] In the foregoing, in the hydraulic cylinder, the rod side chamberpartitioned by the piston 2 within the cylinder body 1 comprises the airchamber A which is communicated with the atmosphere outside the cylinderbody 1 through the communication hole 1 a bored in the cylinder body 1,but in place thereof, though not shown, there can be employed an airspring chamber having a seal construction in which the air chamber A isnot communicated with the atmosphere outside the cylinder body 1.

[0034] And, in a case where the air chamber A is set in the air springchamber, there is an advantage in that when the extended hydrauliccylinder is contracted, contraction of the hydraulic cylinder is quicklyrealized by spring reaction generated in the air spring chamber.

[0035] Further, in the foregoing, the oil seal 8 is disposed adjacent tothe dust seal 6, but in place thereof, though not shown, the lubricationmeans 7 of the present invention may be further provided therebetween.In this case, the outer circumference of the rod body 3 which isso-called dry in the oil seal 8 can be maintained to be wet, which isadvantageous in that further lubrication is secured.

[0036] As described above, in the present invention, there becomespossible to effect expansion and contraction operation for moving therod body in and out of the cylinder body by a supply and discharge ofliquid pressure to the liquid chamber partitioned on the bottom sidewithin the cylinder body. When the hydraulic cylinder is used, forexample, for a forklift, it becomes possible to elevate the fork loadedwith baggage.

[0037] At this time, in a case where the air chamber which is a rod sidechamber partitioned within the cylinder body is communicated with theatmosphere outside the cylinder body, the expansion and contractionoperation is realized without so-called resistance, and further, in acase where the air chamber is set in the air spring chamber having aseal construction, contraction of the hydraulic cylinder extended byspring reaction generated in the air spring chamber can be realizedquickly.

[0038] Further, in the above-described expansion and contraction, thatis, when the rod body is moved in and out of the cylinder body, theouter circumference of the rod body comes in sliding contact with thebearing disposed in the inner circumference of the head member formingan open end of the cylinder body to secure sidability of the rod body tothe cylinder body; the dust seal disposed in the inner circumference ofthe head member prevents dust adhered to the outer circumference of therod body from entering the cylinder body; the lubrication means disposedbetween the bearing and the dust seal forms a lubrication coatingbetween the inner circumference of the bearing and the outercircumference of the rod body to lower sliding friction therebetween;and the oil seal disposed in series with the lubrication means and inthe inner circumference of the head member enables to prevent thelubricating material forming the lubrication coating from escaping tothe external side of the cylinder body to permanently secure lubricationbetween the bearing and the rod body.

[0039] Moreover, with respect to the disposition of the lubricationmeans and the oil seal, a slight change in design of the head memberwill suffice, not requiring a large scaled change in design.

[0040] As a result, according to the present invention, there isprovided a single-acting type hydraulic cylinder subjected to expansionand contraction operation by supply and discharge of liquid pressurefrom the so-called bottom side, which does not bring forth rust orscratch in the outer circumference of the rod body but is optimum forpermanently securing the desired operation.

What is claimed is:
 1. A hydraulic cylinder which is operated to beextended when liquid pressure from outside is supplied to a liquidchamber which is a counter rod side chamber partitioned by a pistonslidably inserted into a cylinder body, the cylinder is operated to becontracted when a supply of liquid pressure to the liquid chamber isreleased whereas a rod body having a proximal end connected to a pistonis moved into the cylinder body due to own weight or load exerting onthe extreme end, and a head member forming an open end of a cylinderbody for moving in and out of the rod body has a bearing for causing theouter circumference of the rod body to sliding contact therewith and adust seal, characterized in that a lubrication means in sliding contactwith the outer circumference of the rod body on the bearing side betweenthe bearing and the dust seal, and an oil seal in sliding contact withthe outer circumference of the rod body on the dust seal side areprovided in series.
 2. A hydraulic cylinder according to claim 1 whereinthe lubrication means comprises a lubricating material such as greasestored in an inner circumferential groove formed in the innercircumference of a head member.
 3. A hydraulic cylinder according toclaim 1 wherein the lubrication means comprises an impregnate materialreceived in an inner circumferential groove formed in the innercircumference of the head member, and a lubricating material impregnatedin said impregnate material.
 4. A hydraulic cylinder according to claim1 wherein a liquid chamber which is a counter rod side chamber and anair chamber which is a rod side chamber are partitioned by a pistonwithin the cylinder body, said air chamber being set in a sealed airspring chamber.